Ammunition includes metallic cases or cartridges, commonly made of brass, which each package a bullet, gunpowder, and primer. The filled cartridge is formed to precisely fit a firing chamber of a firearm.
The manufacture of such brass cartridges is generally known to include annealing a cup of heavy-gauge brass and deep drawing the cup through a multi-stage press arrangement into a final shape of the cartridge. The process for brass further includes ironing cartridge sidewalls during drawing and re-drawing processes to taper the walls with respect to the base, with multiple intermediate anneals conducted between the deep drawing processes.
Brass, having a sufficiently low work hardening rate and low frictional forces, is usable with a multiple annealing and sidewall ironing process, and is suitable for such a deep drawing process including heavy sidewall ironing. Steel, by contrast, has properties such as a high work hardening rate, high strength, and high frictional forces. These properties can lead to galling and scoring issues, which typically result in reduced die life and make heavy sidewall ironing during repeated re-drawing and annealing steps difficult and not generally feasible. Also, while carbon steel has been used to form cartridges, such cartridges included waxing, or application of a protective coating, to prevent rust.
The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.